Hot gas defrost system



Sept. 10, 1957 F. A. SCHUMACHER HOT GAS DEFROST SYSTEM Filed July 11,1956 INVENTOR.

' FRANK A. SCHUMACHER HIS ATTORNEY United States Patent HOT GAS DEFROSTSYSTEM Frank A. Schumacher, Louisville, Ky., assignor to GeneralElectric Company, a corporation of New York Application July 11, 1956,Serial No. 597,222

3 Claims. ((31.62-4) The present invention relates to refrigeratingsystem including means for the hot gas defrosting of an evaporatorcomponent of the system. It is more particularly concerned with a pluraltemperature refrigerating system including a high temperature evaporatorand a low temperature evaporator in series connection in a refrigeratingsystem and improved means for introducing hot gas into the lowtemperature evaporator for the defrosting of that evaporator.

An object of the invention is to provide a refrigerating systemincluding a refrigerant line bypassing the conenser for periodicallyintroducing into the evaporator hot compressed refrigerant for thedefrosting of the evaporator and means in the defrosting circuit forincreasing the load on the compressor and thereby increasing the amountof heat available for defrosting purposes.

Another object of the invention is to provide a plural temperaturerefrigerating system including in series connection an automaticallydefrosting high temperature evaporator and a low temperature or freezerevaporator, the system including a defrosting circuit for introducinghot compressed refrigerant directly from the compressor into the lowtemperature or freezer evaporator and means in that circuit forincreasing the load on the compressor in the form of a flow restrictingmeans in heat exchange relationship with the freezer evaporator.

Further objects and advantages of the invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize the invention will be pointed out with particularity in theclaims annexed to and forming part of this specification.

In carrying out the objects of the present invention there is provided arefrigerating system comprising a compressor, a condenser, a flowrestricting element and an evaporator connected in series refrigeratingcircuit. For defrosting the evaporator there is included a valvecontrolled conduit bypassing the condenser and the flow restrictingmeans or elements connected to the condenser so that hot compressedrefrigerant can be conducted directly from'the compressor to theevaporator for defrosting purposes. The defrosting circuit also includesa fixed restrictor ahead of the evaporator being defrosted forincreasing the load on the compressor and thereby increasing the heatavailable for defrosting purposes. In the preferred modification of thepresent invention the refrigerating system includes a high temperatureselfdefrosting evaporator and a low temperature or freezer evaporatorincluding a flow restriction between the two evaporators, this flowrestriction comprising part of the defrosting circuit as means forproviding the desired load on the compressor during the defrostingcycle.

For a better understanding of the invention reference may be had to theaccompanying drawing in which:

Fig. 1 is a view of a portion of a refi'igerator incorporating anembodiment of the present invention, and

Fig. 2 is a schematic illustration of a refrigerating system employed inthe refrigerator of Fig. 1.

Patented Sept. 10, 1957 Referring to the drawing there is shown atwo-temperature refrigerator which includes a frozen food compartment 2and a fresh food compartment 3. The refrigerating system employed tomaintain these two compartments at their proper operating temperaturesis shown schematically in Fig. 2. This system includes a hermeticallysealed motor-compressor unit 5 and a condenser 6. The system furtherincludes a high temperature evaporator 7 which is disposed-within thefresh food compartment 3 for cooling this compartment and a lowtemperature evaporator 10 for cooling the freezer compartment. The lowtemperature evaporator of the flooded type comprises tubing arranged ingenerally serpentine form connected to a header 13 and secured, in amanner well known in the art, to the exterior of the liner 11 formingthe freezer compartment 2. During the normal refrigerating cycle,refrigerant is supplied from the condenser 6 through a capillary tube 12to the high temperature evaporator 7. From the'high temperatureevaporator 7 the refrigerant flows through a restricted conduit 14 andan injector 15 into one of the lower passes 16 of the serpentine freezerevaporator 10. If desired, a Weighted valve 18 may be included tomaintain normal pressure differential between the evaporators. Therestricted tubing 14 and the injector 15 (and the weighted valve 18 ifused) serve to maintain an operating pressure differential between thehigh temperature evaporator 7 and the low temperature evaporator 10 andthe restricted tubing 14 is brazed or otherwise secured to the bottomwall of the liner 11 for the purpose of accelerating the rate offreezing of water in freezing trays placed in this portion of the lineras is more fully described and claimed in my prior Patent 2,728,198,issued December 27, 1955, and assigned to the same assignee as thepresent invention. Vaporized refrigerant is returned to the compressor 5from the header 13 through suction line 17, thus completing a normalseries refrigerating circuit.

The normal operation of the system is controlled by the switch 19 whichis adapted to engage contacts 20 in a line 21 through which power issupplied to the motor compressor unit 5. The switch 19 is actuated by abellows 22 in response to the temperature of the high temperatureevaporator 7 by means of a thermostatic bulb 23 positioned in contactwith the evaporator 7. Accordingly the normal or refrigerating operationof the system is controlled hy the temperature of the high temperatureevaporator 7. To prevent the accumulation of frost on the hightemperature evaporator 7 disposed within the fresh food compartment 3,the switch 19 is arranged to'energize the compressor unit 5 only afterthe high temperature evaporator 7 has attained a temperature abovefreezing to assure the melting of any frost which has collected on thisevaporator and to de-energize the compressor unit 5 when this hightemperature evaporator 7 has reached a subfreezing temperature in theneighborhood of or close to that sought to be maintained in the freezercompartment 11.

Due to the fact that the freezer compartment 2 is separate and insulatedfrom the fresh food compartment 3 the temperature of that compartmentwill fluctuate only a few degrees during the on and off cycles of thecompressor unit 5 even though the high temperature evaporator 7subjected to the higher temperatures in the fresh food compartment 3will exhibit a temperature change over range from approximately 0degrees F. to 35 to 37 degrees F. Since the freezer evaporator 10continuously operates well below freezing temperatures there is agradual accumulation of frost within the freezer compartment 2 or morespecifically on the walls of the a liner 11 forming this compartment. Asthis layer of frost has an insulating eifect reducing the efliciency ofthe evaporator 10, it is necessary to remove this frost from time totime in order to prevent too serious a reduction in the operatingefiiciency of the system. In accordance with the present invention meansare provided for periodically introducing into the freezer evaporatorhot compressed refrigerant directly from the compressorin order thatthis low temperature evaporator can be heated by the hot gas todefrosting temperatures. Since it is desirable that the defrosting ofthe low temperature evaporator 10 take place as quickly as possible inorder to prevent damage to the contents of the freezer compartment z,there is provided in accordance with the present invention means forincreasing the load on the compressor unit 5 during the defrostingoperation and thereby iucreasingth'e amount of heat available in the hotgas for defrosting purposes. r r V 'l'n order to introduce hotcompressed refrigerant into the low temperature evaporator 10.. thereprovided a conduit 27-bypassing the condenser 6, the flow restrictingelement -12Han d-the high temperature evaporator 7 and connectingtheoutlet of the compressor 5 to the line leadi-ng from the hightemperature evaporator 7 to the low temperature evaporator 10. Asolenoid operated valve 28 is. provided in the bypass line '27 and thisvalve is normally closed so that during the operation of therefrigerating system on the refrigerating cycle, the flow of refrigerantfrom the compressor 5 is through the condenser -6 to the evaporators inseries.

The operation of .the solenoid valve 28 is controlled by a switch 30which also by means'of lines 31 energizes the compressor unit -5whenever the solenoid valve 28 is energized and open. The switch 30 maybe of any suitable type. For example it may be a manually controlledswitch whereby the user of the refrigerator manually effects thedefrosting operation of the refrigerating system. Alternatively it maybe a timer control switch so that the refrigerating system is operated,on the defrosting cycle periodically as for example once a day.

Whenever theswitch 30 energizes the solenoid valve v 28 to open thisvalve, the energization of the compressor unit 5 ,causes hot compressedrefrigerant gas to. flow through the bypass line 27 directly to thefrozen food or low temperature evaporator 10; By including therestrictions 14 and 15 in the hot gas .circuit, the restrictionincreases the pressure against which the compressor unit 5 must pump andthereby increases the watt input to the compressor motor .cooled by thecirculating refrigerant substantially over the input in the case where anonrestricted hot gas flow is employed. This increased wattage resultsin more energy being transmitted to the circulating refrigerant,speeding up thedefrosting of the frozen food evaporator 10 or in otherwords decreasing .the time necessary for frost removal.

As an example of the manner in which the present inventionmay be :putinto .eifect, the restriction in thebypass pr defrost circuit formed bythe restricted conduit 14 in heat exchange relationship with the bottomof the liner 11 and ,by the injector 1 5 effected an increase in themotor running watts from 300 to 337 watts at the start of the defrostcycle and from 360 to 450 watts at the end of the de os ope ation whenthe ubes .comp the p rator 10 were approximately 40 F. The restrictionin this case was formed by the injector consisting .of 5 /2 inches of.095 inside diameter tubing and by the tubing 14 which .was .171)"inside diameter and approximately seven f e i lengt r It be'noted thatduring the defrosting operatien no valve means are provided to preventflow of refrigerant thrqughthe normal. circuit that ,is through thecondenser 15, therestrictor 12 and the high temperature evaporator -7-;F o r that reason the restriction provided in the defrost circuit up.to the point where the conduit 27 connects to the system between thehigh temperature evaporator and the low temperature evaporator is lreptat a although if desired a restriction 35 having a low restrictive valuemay be introduced into the line 27. While such a 4 restriction will addto the total restrictive value provided by the line 14 and the injector15, it is necessary that the restrictive value of the restrictor 35 bekept below that which will cause a substantial portion of therefrigerant to flow through the condenser 6. For that reason there ispreferably employed only the restricting means forming part of thenormal refrigerating circuit since the presence of these restrictingmeans in the defrosting circuit does not affect the restrictive balancebetween the normal and defrosting circuits or in other words will loadthe compressor unit Without causing an excessiveam'ount of thecompressed refrigerant .to flow through the condenser 6 instead of thebypass line 27. While there has been shown and described a specificembodiment of the present invention, it is not desired that theinvention be 'limited to the particular construction shown anddescribed. For example the use of restriction in the hot gas bypass lineis not necessarily confined to the defrosting of a low temperatureevaporator in a plural evaporator circuit although the invention isparticularly advantageous as applied to such systems andspecifically tosystems such as that disclosed in which the low temperature evaporatoris of the flooded type and includes an injector such as injector 15.With such an arrangement it has been found that the hot gas introducedinto the What, I claim as new and desire to secure by Letters Patent .ofthe United States is:

l. A refrigerating system comprising a compressor, a pondenser, a'florvrestricting element, a hightemperature evaporator for cooling .a freshfood compartment, a low temperature evaporator for maintaining a frozenfood compartment at subrfreezing temperatures, said compressor,condenser, flow restricting element, high temperature evaporator and lowtemperature evaporator being connected in series in a closedrefrigerating .circuit, control means responsive to thejcemperature .ofsaid high temperatureevaporator for startingsaidnompressor only vwhensaid high temperature evaporator has attained a temperature abovefreezing to assure defrosting of said high temperavtpreevaporator priorto energization of saidscompressor and means for periodically.defrosting said low temperatureevaporator including a .conduitbypassing said condenser, flow restricting .element and high temperatureevaporator and connecting said compressor directly to the inlet to saidloyv temperature evaporator for the introduction of -hot gas into .said.low temperature evaporator, a valve in said .cpnduitrcontrolling theflow of refrigerant therethgough, control meaps for controlling thepperation of said valve and energizing .said compressor ,when said valveis open, and a restrictor having a lower restn'gtive value than saidflow restricting element for increasing the amount .of heat available inthe hot low temperature evaporator. V

2. A refrigerating system comprising a compressor, a condenser, afirstflow restricting elemenha high temperature evaporator fgr cooling ,9.fresh food compartment, a second flow restricting element, a lowtemperature evaporator for maintaining a frozen food compartment atsubfreezingotemperatures, said compressor, condenser, first gas fordefrosting said flow restricting element, high temperature evaporator,

second flowrestricting .element andv low temperature .evaporatorheingconnected in series in a closed refrigeratns c cui goon-91 m ans responiv to the temperature of sa s lhi h tep nra g e evaporate: o st. inssaid q pressor rl vt e sa d .h sh em er t re-sac um ha attained a teerature above freezing to assure defrosting of'said high temperatureevaporator prior to energization 9 sa d compresso and mean f r p fiqd sv ros said low perature evaperator including ,a condpit by- Pa sin sad et m n fi s flew r st ic in el m n and high tmperawr'e Wanderers renew ns i wows sor to the inlet to said second flow restricting element forthe introduction of hot gas through said second element into said lowtemperature evaporator, a valve in said conduit controlling the flow ofrefrigerant therethrough, control means for controlling the operation ofsaid valve and energizing said compressor when said valve is open, saidsecond element placing a load on said compressor and thereby increasingthe amount of heat available in the hot gas for defrosting said lowtemperature evaporator, said second element being in heat exchangerelationship with at least a portion of said low temperature evaporator.

3. A refrigerating system comprising a compressor, a condenser, a firstflow restricting element, a high temperature evaporator for cooling afresh food compartment, a second flow restricting element having alesser restrictive value than said first element, a flooded lowtemperature evaporator for maintaining a frozen food compartment atsub-freezing temperatures, said compressor, condenser, first flowrestricting element, high temperature evaporator, second flowrestricting element and low temperature evaporator being connected inseries in a closed refrigerating circuit, control means responsive tothe temperature of said high evaporator has attained a temperature abovefreezing to assure defrosting of said high temperature evaporator priorto energization of said compressor and means for periodically defrostingsaid low temperature evaporator including a conduit bypassing saidcondenser, first flow restricting element and high temperatureevaporator and connecting said compressor to the inlet to said secondelement for the introduction of hot gas into said low temperatureevaporator, said second element including an injector for effectingcirculation of refrigerant in said flooded low temperature evaporator, avalve in said conduit controlling the flow of refrigerant through saidconduit, control means for controlling the operation of said valve andenergizing said compressor when said valve is open, said secondrestrictive element having restrictive valve sufficient to load saidcompressor and thereby increase the amount of heat available in the hotgas for defrosting said low temperature evaporator.

References Cited in the file of this patent UNITED STATES PATENTS2,458,589 Groat Jan. 11, 1949 2,765,633 Mufiiy Oct. 9, 1956

